(1) Field of the Invention
The present invention relates to the manufacture of books and, particularly, to the assembling of folded pages into an ordered stack which defines an inner book. More specifically, this invention is directed to book assembly apparatus wherein pre-printed folded sheets are individually withdrawn from magazines arranged in a serial array and deposited, one on top of another, on a conveyor and, especially, to a feeder device for withdrawing a folded sheet from a magazine and delivering the thus withdrawn sheet to an assembly conveyor. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
In the manufacture of books, folded pre-printed sheets are assembled, i.e., collated, into inner books which are built up in the proper page sequence on a collecting conveyor. This assembly operation requires the use of a plurality of serially arranged feeders which withdraw individual folded sheets from magazines in which they have been stacked. Such feeders, in the prior art, include a withdrawal drum and an intermediate support on which the withdrawn sheets are temporarily supported before they are deposited on a moving stack being built up on the collecting conveyor. Prior art sheet feeders also include a sheet separating device which is operated in synchronism with the withdrawal drum. The separating device has typically comprised a suction element for applying force to an edge region of the lowermost sheet in the stack to bend the edge region out of the plane of the sheet. A gripping mechanism on the withdrawal drum engages the thus separated edge region of the folded sheet and pulls the sheet from the bottom of the stack.
The folded sheets which are to be assembled into the inner book are situated in the stacked magazines with their edges in alignment, such alignment being insured by delimitation defining elements of the magazine. In the prior art, the magazine base is provided with an opening through which individual sheets may be withdrawn. The suction element which causes separation of the edge region of the lowermost sheet from an adjacent butting sheet in the stack operates in this opening and, customarily, bends or tilts a portion of the spine fold region of the sheet to a position where it may be engaged by a withdrawal drum gripper. The stack of folded sheets in the magazine, in the front edge region thereof, may be supported during the withdrawal phase of the operating cycle by stack lifters which move cyclically in synchronism with the suction elements, the stack lifters thereby preventing sagging of the stack when the partially deflected lowermost sheet is withdrawn from the magazine.
The collecting conveyor of prior art assembling machines has typically comprised a collecting channel aligned transversely with respect to the direction of withdrawal of the folded sheets from the magazines. Drivers, conventionally in the form of fingers which extend from a moving chain, project through a slot in the bottom of the collecting channel and impart movement to, while simultaneously causing edge alignment of, the ordered stack of folded pages which define the inner book being assembled. The drive fingers are sufficiently long so as to engage folded sheets which have been withdrawn from magazines and are supported above the collecting channel on the intermediate supports whereby motion in a second direction will be imparted to such withdrawn sheets and they will fall off the intermediate supports onto the moving stack. Alignment of the stack of folded sheets on the collecting conveyor is also accomplished by providing the collecting channel with an aligning edge or fence which arrests movement of the withdrawn sheets in the direction of withdrawal from the magazines.
Assembling machines which operate with a change of direction of the folded sheets withdrawn from the magazines, as briefly described above, are exemplified by the apparatus disclosed in published German Patent Application 14 86 744. In an effort to increase production rates of assembling machines of this type, mechanisms for accelerating the speed of motion of the folded sheets after withdrawal from the magazines may be employed. Such acceleration is accomplished, in the apparatus of German Application 14 86 744, through the use of reciprocating tables as the intermediate supports for the withdrawn sheets. Acceleration systems, however, increase the cost and complexity of the assembling apparatus and reduce the reliability thereof.
Assembling machines which do not require a change in the direction of motion of the folded sheets withdrawn from the magazines are also known. This type of assembling machine, as exemplified by the disclosure of U.S. Pat. No. 3,825,247 utilizes a rotational withdrawal system. Such rotational withdrawal systems employ a withdrawal drum having an axis of rotation oriented transversely with respect to the direction of movement of product on the collecting conveyor. The folded sheets are separated, closed folded edge first, from their respective magazines by a combination of pneumatic and mechanical means, rotated through an angle of 180.degree. and deposited on the collecting conveyor.
Withdrawal systems of the type generally described in U.S. Pat. No. 3,825,247, i.e., systems with gripper drums which withdraw the folded sheets from the magazines and deposit the same in the direction of movement of the collecting conveyor, are an obvious choice if production rate is to be maximized. However, such systems have in practice been found to be of limited utility due to alignment problems. That is, in the practice of the book assembling technique of U.S. Pat. No. 3,825,247, the spines of the folded sheets will face in the downstream direction of the collecting conveyor and, accordingly, an opposite edge of each sheet will be contacted, and brought into alignment, by the drive fingers of the collecting conveyor. The folding process, however, inherently leads to inaccuracies, i.e., the two trailing edges of each folded sheet are often not in precise registration. Thus, the collecting conveyor drivers will cause the "longer" pages of each folded sheet to be aligned leading to misalignment of the folded spine edges and thus to displacement of the printed images from their desired position in the completed book.
It must also be noted that prior art feeders of the type disclosed in U.S. Pat. No. 3,825,247, which utilize gripper drums and associated suction elements, are located under the magazines. As may be seen from FIG. 3 of the patent, this positioning requires the bending of the folded sheets downwardly over a bottom edge or lip of the magazine. This has, in practice, been found to lead to failures to feed sheets, particularly when the sheets are comprised of paper with a relatively high inherent rigidity. Conversely, when the applied suction force is sufficiently high to ensure downward bending of the lowermost folded sheet in the magazine, the freshly printed folded sheets are often disfigured by marks left thereon by the separating apparatus.
When processing folded sheets which are characterized by low inherent rigidity, there is a risk that at least the second lowermost folded sheet in the magazine will be entrained by the lowermost sheet during withdrawal. Any motion imparted to such an adjacent sheet in the magazine will, at the very least, cause such sheet to become warped, a condition known in the art as "roll-up", leading to subsequent misfeed. Such feed malfunctions are particularly prevalent during the separation of folded sheets which are open at three sides and include inserted quarter sheets. In fact, depending on paper quality, print quality and climatic conditions, there is an inherent risk that the sheet located adjacent to the folded sheet being withdrawn from the magazine will either be "rolled-up" or actually be fully withdrawn as a result of friction between the top page of the lowermost sheet and the bottom page of the adjacent sheet or as a result of the attraction between the abutting pages caused by a build-up of static electricity or as a consequence of adherence between the print on the two facing pages. Either a missing sheet malfunction resulting from a rolled-up sheet or a double feed is highly undesirable in that it will lead either to waste or a production stoppage.